A unique glycoprotein, present in normal fibroblasts but absent in transformed cells, was revealed by cell surface label with galactose oxidase-NaB3H4, and termed "galactoprotein a" (Gap a). In contrast, the label in one glycoprotein increased significantly in transformed NILpy cells, and termed "galactoprotein b" (Gap b). A similar glycoprotein present in various nontransformed fibroblasts and deleted in various transformed cells has been observed in various laboratories and variously termed LETS, Zeta, SF-A, CSP, etc. The Gap a increased greatly on cell contact, at G1 phase of the cell cycle, and interacted with Con A, RCA, fibrinogen and collagen. The Gap b fraction of NILpy cells contained a glycoprotein whose mobility on gel electrophoresis was faster than Gap b and called Gap bT which is regarded as transformation-specific glycoprotein. This research will continue the study of isolation and characterization of Gap a, Gap b, Gap bT, or the related cell surface molecule in hamster NIL or rat NRK cells and their transformed counterparts. We will investigate (1)\the chemical characterization of glycopeptides, oligosaccharides and peptide fragments from Gap a and b, (2)\the structural modification of the molecules associated with cell contact, cell cycle, and virus-induced transformation, (3)\the mechanism of the interaction of Gap a and b on cell surface components and (4)\the structural difference between Gap a present on cells and those in serum (CIg). The Gap a and b may play important roles in determination of cellular interaction, adhesion and expression of transformed phenotype.